As we have seen thus far, the oscillation of the first laser was achieved by Maiman from Hughes in California in 1960. After that, various types of lasers were developed one after another. By 1962, four research groups in the U.S. achieved laser oscillation using the first laser diode almost simultaneously. However, this early laser diode employed pulse oscillation at liquid nitrogen temperature. If the laser could be operated only at liquid nitrogen temperature with pulse oscillation, the practical application of the laser would have remained seriously limited. Therefore, firms, universities, and research institutes competed to create a viable continuous wave operation of the laser diode at room temperature.